Re: Process Scheduling Issue using sg/libata

[Mark Lord <liml@rtr.ca>]

Fajun Chen wrote:
>..
> I verified your program works in my system and my application works as
> well if changed accordingly. However, this change (indirect IO in sg
> term) may come at a performance cost for IO intensive applications
> since it does NOT utilize mmaped buffer managed by sg driver.  Please
> see relevant sg document below:
> http://sg.torque.net/sg/p/sg_v3_ho.html#id2495330
> http://sg.torque.net/sg/p/sg_v3_ho.html#dmmio
> As an example, sg_rbuf.c in sg3_util package uses SG_FLAG_MMAP_IO flag
> in SG_IO. Please see source code attached. I also noticed that
> MAP_ANONYMOUS is NOT used in mmap() call in sg_rbuf.c, which may not
> be desirable as you pointed out in previous emails. So this brings up
> an interesting sg usage issue: can we use MAP_ANONYMOUS with
> SG_FLAG_MMAP_IO flag in SG_IO?
..

The SG_FLAG_MMAP works only with /dev/sg* devices, not /dev/sd* devices.
I don't know which kind you were trying to use, since you still have
not provided your source code for examination.

If you are using /dev/sg*, then you should be able to get your original mmap()
code to work.  But the behaviour described thus far seems to indicate that
your secret program must have been using /dev/sd* instead.

Cheers